In an engine of an automobile vehicle, in order to reduce the NOx contained in the exhaust gas thereof, is provided an exhaust gas recirculation apparatus recirculating the exhaust gas to the intake side thereof. An exhaust gas recirculation passage of the apparatus is provided with an EGR valve (“Exhaust Gas Recirculation” valve), and the EGR valve is controlled based on the driving information or the like of the engine. If high-temperature exhaust gas is recirculated to the intake side thereof as it is, the efficiency of the engine becomes deteriorated, and thus, in general, the exhaust gas recirculation passage is provided with an EGR cooler for cooling the high-temperature exhaust gas.
Exhaust gas passing through the EGR valve contains sulfur oxides coming from a fuel system, and nitrogen oxides and particulate matter (PM) such as soot and the like which are produced by combustion. Therefore, those substances are also introduced in the exhaust gas recirculation passage, and they adhere to a valve rod of the EGR valve. When the soot and the like are deposited over the valve rod (the matter deposited thereover is referred to as “deposit”), they can cause trouble in normalfunction of the valve rod. In order to solve the troubles caused by the adhesion of the particulate matter to the valve rod, a technology is disclosed (Patent Document 1), arranged to prevent the soot and the like from being caught by the inner surface of a bearing, by providing a deposit relief groove formed by reducing the diameter of the valve rod on the valve rod side in the portion of the valve rod sliding in the bearing such that the soot and the like are collected in the deposit relief groove.
Patent Document 1: JP-A-2002-285918
The technology disclosed in Patent Document 1 aims to deposit the soot and the like within the deposit relief groove; however, the particulate matter does not necessarily uniformly adhere to the surface of the deposit relief groove. When the matter is heavily deposited at one site in the groove or the groove is filled up with the deposit, the deposit causes trouble in normal operation of the valve. Further, when the soot and the like are deposited over the shouldered portion between the bottom of the reduced-diameter section forming the deposit relief groove and the outer surface of the valve rod, and the deposit becomes massive, it can prevent the valve rod from operating.
Otherwise, a proposal is made to provide a filter through which a valve rod extends on the exhaust gas passage side of a bearing and actively scrape the soot and the like adhered to the valve rod using the filter. However, when the deposition of the scraped soot, etc. continues over a valve head provided at the end of the valve rod and the deposit increases in volume to exceed the external diameter of the valve rod, the deposit becomes a cause of the malfunction of the valve rod.
The present invention has been accomplished to solve such a technical situation, and an object of the present invention is to prevent the malfunction of an EGR valve exposed to exhaust gas even if soot and the like adhere to the valve rod of the EGR valve.